Chemistry: analytical and immunological testing – Hydrogen – per se
Reexamination Certificate
1999-01-15
2001-07-24
Alexander, Lyle A. (Department: 1743)
Chemistry: analytical and immunological testing
Hydrogen, per se
C436S147000, C422S083000, C422S088000, C073S023200, C073S031060
Reexamination Certificate
active
06265222
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a micro-machined thin film hydrogen sensor device, and a method of making and using the same.
2. Description of the Related Art
Hydrogen gas is used in variety of applications ranging from semiconductor thin film processing to rocket fuel in the aerospace industry. The combustible nature of hydrogen however, makes its detection vitally important.
About one-half of all the sensors used to measure hazardous gases measure hydrogen. The bulk of these systems utilize as the detector element a Group VIIIB metal element (Ni, Pd, Pt) that is heated to catalytically oxidize the hydrogen, with the resulting change in heat load being the measured parameter for determination of the presence of hydrogen.
Sensors of such “hot wire” type have cross-sensitivity to other easily oxidized materials, such as alcohols and hydrocarbons. Such easily oxidized materials are common components of gases in a semiconductor-manufacturing environment, and in such application the result is frequent occurrence of false alarms.
Since the current generation of hot wire sensors require an oxidation reaction for operation, such sensors are unable to detect hydrogen when it is present in inert gas streams or environments which are not of a character to support oxidative reaction. This is a severe deficiency of such hot wire sensors and limits their applicability and utility.
It would be a significant advance in the art to provide a sensor overcoming the aforementioned deficiencies of current hot wire sensors.
Another class of sensors includes metal-insulator semiconductor (MIS) or metal-oxide- semiconductor (MOS) capacitors and field effect transistors, as well as palladium-gated diodes. In general however, these sensors are limited to detecting low concentrations of hydrogen.
Because hydrogen is used in such a wide variety of environments, it is desirable to have a sensor that will be reproducible and specific to hydrogen, even with varying concentration of background gases such as oxygen, water and other contaminants.
It is also desirable to have a solid state sensor that has no moving parts, has a response time on the order of seconds, would operate with minimum power consumption, does not require frequent calibration, and could be used in a hand-held portable instrument.
The disclosures of the foregoing references are hereby incorporated herein by reference in their entireties, together with the disclosures of the following pending United States patent applications: U.S. patent application Ser. No. 09/042,698 filed Mar. 17, 1998 in the names of Gautam Bhandari and Thomas H. Baum for “Hydrogen Sensor Utilizing Rare Earth Metal Thin Film Detection Element, now U.S. Pat. No. 6,029,500” and U.S. patent application Ser. No. 09/081,957 filed May 19, 1998 in the name of Glenn M. Tom for “Piezoelectric Quartz Crystal Hydrogen Sensor, and Hydrogen Sensing Method Utilizing Same, now U.S. Pat. No. 6,029,500.”
It therefore is one object of the present invention to provide an improved hydrogen sensor.
It is another object of the invention to provide a hydrogen sensor that senses the presence of hydrogen in a reproducible and hydrogen-specific manner.
It is another object of the invention to provide a hydrogen sensor that senses the presence of hydrogen in a reproducible and hydrogen-specific manner, even with varying concentration of background gases such as oxygen, water and other contaminants.
It is yet another object of the present invention to provide a solid state hydrogen sensor that has no moving parts, has a response time on the order of seconds, operates with minimum power consumption, does not require frequent calibration, has a large dynamic detection range, and can be readily embodied as a hand-held portable instrument.
Other objects and advantages of the present invention will be more fully apparent from the ensuing disclosure and appended claims.
SUMMARY OF THE INVENTION
The present invention relates in one aspect to a hydrogen sensor, comprising a hydrogen-interactive thin film sensor element on a micro-hotplate structure.
The hydrogen-interactive thin film sensor element of such sensor may comprise a hydrogen-interactive thin film (i) arranged for exposure to an environment susceptible to the incursion or generation of hydrogen and (ii) exhibiting a detectable change of physical property when the hydrogen-interactive thin film is exposed to hydrogen. Such detectable change of physical property may comprise optical transmissivity, electrical resistivity, electrical conductivity, electrical capacitance, magneto-resistance, photoconductivity, and/or any other detectable property change accompanying the exposure of the thin film sensor element to hydrogen. The hydrogen sensor may further include a detector constructed and arranged to convert the detectable change of physical property to a perceivable output, e.g., a visual output, auditory output, tactile output, and/or auditory output.
In one preferred embodiment, the hydrogen-interactive thin film is overlaid by a hydrogen-permeable material protecting the rare earth metal thin film from deleterious interaction with non-hydrogen components of the environment being monitored, such as nitrogen, oxygen, ammonia, hydrocarbons, etc. The protective-overlayer may include a metal such as Pd, Pt, Ir, Rh, Ag, Au, Co, and/or alloys thereof.
The micro-hotplate structure in the sensor of the invention may be advantageously constructed and arranged for selectively heating the hydrogen-interactive thin film gas sensor element according to a predetermined time-temperature program, e.g., involving cyclic heating of the hydrogen-interactive thin film gas sensor element by the micro-hotplate structure.
The invention relates in another aspect to a hydrogen sensor device, comprising:
a micro-hotplate structure;
a hydrogen-interactive thin film gas sensor element on the micro-hotplate structure; and
a detector for sensing a detectable change of physical property of the film in exposure to hydrogen and generating a correlative output indicative of hydrogen presence.
A power supply may be provided in such device and may be constructed and arranged for actuating the micro-hotplate structure during and/or subsequent to sensing the detectable change of physical property of the rare earth metal thin film in exposure to hydrogen, and/or for energizing the detector.
A further aspect of the invention relates to a method of fabricating a hydrogen sensor on a substrate, comprising:
constructing on the substrate a micro-hotplate structure; and
forming on the micro-hotplate structure a hydrogen-interactive thin film that in exposure to hydrogen exhibits a detectable change of at least one physical property, and wherein the hydrogen-interactive thin film is arranged to be heated by the micro-hotplate structure.
A still further aspect of the invention relates to a method of detecting hydrogen in an environment, comprising:
providing a hydrogen sensor device comprising a hydrogen-interactive thin film operatively coupled with a micro-hotplate structure for selective heating of the hydrogen-interactive thin film, with the hydrogen-interactive thin film being arranged for exposure to the environment and exhibiting a detectable change of physical property when the hydrogen-interactive thin film is exposed to hydrogen;
exposing the hydrogen-interactive thin film to the environment;
outputting said detectable change of physical property when the presence of hydrogen in the environment is detected; and
selectively heating the hydrogen-interactive thin film by the micro-hotplate structure during and/or subsequent to detection of hydrogen in said environment, to enhance the performance of the hydrogen-interactive thin film for detection of hydrogen.
Other objects and advantages of the invention will be more fully apparent from the ensuing disclosure and claims.
REFERENCES:
patent: 3732076 (1973-05-01), Toy et al.
patent: 6006582 (1999-12-01), Bhandari et al.
Bhandari Gautam
DiMeo, Jr. Frank
Alexander Lyle A.
Hultquist Steven J.
Zitzmann Oliver A. M.
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